1. Field of the Invention
The present invention relates to a reduced-pressure processing apparatus which can perform two reduced-pressure processes continuously or only one of these processes selectively.
2. Description of the Related Art
A reduced-pressure processing apparatus is known which is designed to perform etching, ashing, film-forming and the like under a reduced pressure. The apparatus comprises a processing chamber and two load-locking chambers connected to both sides of the processing chamber. A workpiece is processed under a reduced pressure in the processing chamber. The load-locking chambers are used to shield the processing chamber from the atmosphere while a workpiece is being moved into, and removed from, the processing chamber.
A reduced-pressure processing apparatus of another type called "in-line type" is known (see U.S. Pat. No. 4,825,808), which is designed to perform different processes continuously. The in-line type reduced-pressure processing apparatus comprises a plurality of processing chambers and a plurality of load-locking chambers. The processing chambers are arranged in a row. Each load-locking chamber, except two, is located between and connected to any two adjacent processing chambers. The remaining two load-locking chambers are connected to the first processing chamber and the last processing chamber, respectively.
A reduced-pressure processing apparatus of another type called "multi-chamber type" is also known (see U.S. Pat. No. 4,785,962), which is designed to perform different processes continuously, as well. The multi-chamber type reduced-pressure processing apparatus comprises a hollow cylindrical load-locking chamber and a plurality of processing chambers arranged around the load-locking chamber and connected thereto.
In each of the three types of reduced-pressure processing apparatuses, each processing chamber is connected to a load-locking chamber by means of an open/close mechanism such as a gate valve.
The apparatuses of three types described above are disadvantageous in the following respects.
In the apparatus of the first-mentioned type, a workpiece cannot be continuously subjected to two or more processes. To continuously subject the workpiece to two processes, for example, two apparatuses of this type must be used in combination. If two or more apparatuses are used for this purpose, any common component of each apparatus cannot be utilized for any other apparatus, too. Further, the use of two or more apparatuses is not economical and requires a large floor space.
The in-line type apparatus must usually perform as many processes as the processing chambers it has. In other words, a workpiece cannot be removed from the apparatus into the atmosphere before it is processed in all processing chambers. The use of the apparatus is inevitably limited.
As has been indicated, the multi-chamber type apparatus has one load-locking chamber and two or more processing chambers arranged parallel to each other and connected to the load-locking chamber. Hence it is possible to perform a process in a selected one of the processing chambers or more processes in selected ones of the processing chambers, if the sequence control is altered appropriately. The multi-chamber type apparatus has a drawback, however. Most apparatuses of the multi-chamber type has four processing chambers at the least, which are connected to the single load-locking chamber. The load-locking chamber therefore has a great volume. It takes much time to evacuate the load-locking chamber, particularly when only one or two processes are performed on a workpiece, inevitably decreasing the process throughput. A multi-chamber type apparatus having only processing chambers occupies a floor space which is large for the number of the processing chambers, since its load-locking chamber has a great volume in most cases.